MongoDB – Fix "Failed to convert from type String to type Date"?

To fix the "Failed to convert from type String to type Date" error in MongoDB, use $dateFromString in an aggregation pipeline. This operator converts a date/time string to a proper Date object that MongoDB can process.

Syntax

db.collection.aggregate([
    {
        $project: {
            fieldName: {
                $dateFromString: {
                    dateString: "$stringDateField",
                    format: "%d-%m-%Y",
                    timezone: "UTC"
                }
            }
        }
    }
])

Sample Data

db.demo619.insertMany([
    {"DueDate": "10-10-2020"},
    {"DueDate": "12-01-2019"},
    {"DueDate": "28-10-2010"}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e99d7846c954c74be91e69e"),
        ObjectId("5e99d7996c954c74be91e69f"),
        ObjectId("5e99d7ab6c954c74be91e6a0")
    ]
}

Display all documents from the collection ?

db.demo619.find();

{ "_id": ObjectId("5e99d7846c954c74be91e69e"), "DueDate": "10-10-2020" }
{ "_id": ObjectId("5e99d7996c954c74be91e69f"), "DueDate": "12-01-2019" }
{ "_id": ObjectId("5e99d7ab6c954c74be91e6a0"), "DueDate": "28-10-2010" }

Example: Convert String to Date

Convert the string dates to proper Date objects using $dateFromString ?

db.demo619.aggregate([
    {
        $project: {
            DueDate: {
                $dateFromString: {
                    dateString: '$DueDate',
                    timezone: 'America/New_York'
                }
            }
        }
    }
]);

{ "_id": ObjectId("5e99d7846c954c74be91e69e"), "DueDate": ISODate("2020-10-10T04:00:00Z") }
{ "_id": ObjectId("5e99d7996c954c74be91e69f"), "DueDate": ISODate("2019-01-12T05:00:00Z") }
{ "_id": ObjectId("5e99d7ab6c954c74be91e6a0"), "DueDate": ISODate("2010-10-28T04:00:00Z") }

Key Points

• $dateFromString automatically detects common date formats like "MM-dd-yyyy".
• Use the format parameter to specify custom date formats if needed.
• The timezone parameter handles timezone conversion during parsing.

Conclusion

The $dateFromString operator in MongoDB aggregation pipelines effectively converts string representations of dates into proper Date objects, resolving type conversion errors. This ensures your date operations work correctly with proper Date types.